Download Chapter 4 - The Cybermaze

Chapter 4: Making
Sense of The Universe:
Matter, Energy &
Gravity
What Is Matter?
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Matter is the “stuff” that makes up
our “things”
Matter is composed of atoms and their
constituents
These “elements” combine to form
the molecules of life
Matter has MASS - Mass is an intrinsic
property of matter
What Is Energy?
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Energy comes in different forms:
- Kinetic (motion)
- Potential (stored)
- Radiative (electromagnetic)
Mass can be turned into Energy
Energy can become Mass
E=mc2
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Energy can change type but not be created
or destroyed.
Matter is composed of atoms
The Periodic Chart
These elements all have unique chemical properties, based on the
number of protons, neutrons and electrons they are composed of.
If you add or remove neutrons from the most common form of an
element, you create Isotopes.
Stripping electrons from an atom is called Ionization.
Phases of Matter
 Solid
 Liquid
 Gas
 Plasma
The state changes as you
increase the temperature
(add energy)
Thermal Energy:
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The collective kinetic energy of many particles
(for example, in a rock, in air, in water)
– Thermal energy is related to temperature but it is NOT the same.
– Temperature is the average kinetic energy of the many
particles in a substance.
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Temperature Scales
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Inc.
Temperature Scales
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Thermal energy is a measure of the total kinetic energy of all
the particles in a substance. It therefore depends on both
temperature AND density.
Example:
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Atoms & Orbits
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Matter appears solid, but is composed of
mostly empty space!
Electrons orbit atoms in clouds, with higher
energy electrons in farther orbits
Atomic Energy States
Potential Energy
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Potential Energy is the energy something
has just because it has mass and is where it
is
Think of a boulder on a hill as an example,
when it rolls down it turns potential energy
into Kinetic Energy
(U=mgh)
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Simply by having mass that can be turned
into energy is potential…
Gravitational Potential
Energy
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In space, an object or
gas cloud has more
gravitational energy
when it is spread out
than when it contracts.
– A contracting cloud
converts gravitational
potential energy to
thermal energy.
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Kinetic Energy
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When mass is moved it is Kinetic
Energy (T=1/2 mv2)
Adding energy to a system, i.e. as
heat, will make the atoms more
energetic and they will move more,
colliding with other atoms – this is
Kinetic Motion
Temperature ~ Energy
Conservation of Energy
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In a closed system, the sum total of the energy is conserved
The Universal
Laws of Motion
Motion
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What is the difference between: Speed,
Velocity & Acceleration?
Speed is a scalar, that means that it is how
fast you go, but without specific direction
Velocity is a vector, it gives speed and
direction
Acceleration is found when an object is
speeding up or slowing down
Formulae
v = Δx/ Δt
a = Δv/ Δt
g = 9.81 m/s2
Mass & Momentum
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Mass is an intrinsic property of matter. The
atomic mass is invariant, regardless of your
gravitational field (or speed)
Weight is a Force, it changes depending on
your gravitational field
Momentum is mass x velocity, it tells you
that big-fast things are harder to stop than
small-slow things.
p = mv
How did Newton change our view
of the universe?
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Realized the same physical
laws that operate on Earth also
operate in the heavens
– one universe
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Discovered laws of motion and
gravity
Much more: experiments with
light, first reflecting telescope,
calculus…
Sir Isaac Newton
(1642–1727)
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Newton’s Laws of Motion
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First Law: An object at rest remains at rest,
and an object in motion remains in motion,
unless acted upon by an external force
Second Law: F = ma = Δp/ Δt
Force depends on rate of change of
momentum.
Third Law: For every force, there is an equal
and opposite force
Conservation of Momentum
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Newton’s laws imply the concept of
conservation of momentum. The total
momentum in a system is conserved.
Angular momentum acts on a body in orbit
around another, held by the gravitational
force. In the absence of net torque, the
angular momentum remains constant.
angular momentum = mvr
Angular momentum conservation also
explains why objects rotate faster as they
shrink in radius.
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Center of Mass
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Because of momentum
conservation, orbiting
objects orbit around
their center of mass.
Newton’s Universal Law of
Gravitation
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Every mass attracts other mass through the force
called gravity
The force of attraction between any two objects is
directly proportional to the product of their masses
The force of attraction between two objects
decreases with the square of the distance between
their centers
Fg = GM1M2/d2
(note that G is the gravitational constant)
What determines the
strength of gravity?
The universal law of gravitation:
1.
Every mass attracts every other mass.
2.
Attraction is directly proportional to the product of their
masses.
3.
Attraction is inversely proportional to the square of the
distance between their centers.
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Newton’s Influence
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Some 70 years after Kepler published his three laws
of orbital motion, Newton was able to explain
“why” they held true!
Science strives to observe, determine relationships
and eventually discover “why” things work the way
they do.
Newton’s laws remained unchallenged until an
upstart named Albert Einstein developed a general
theory of gravity that was more precise in 1905.
How does Newton's law of gravity
extend Kepler's laws?
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Kepler's laws apply to all
orbiting objects, not just
planets.
Ellipses are not the only
orbital paths. Orbits can
be:
– bound (ellipses)
– unbound
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parabola
hyperbola
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How do gravity and energy
together allow us to
understand orbits?
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Total orbital energy stays constant.
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Total orbital energy
(gravitational +
kinetic) stays constant
if there is no external
force.
Orbits cannot change
spontaneously.
How does gravity cause tides?
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Moon's gravity pulls harder on near side of Earth than on far side.
Difference in Moon's gravitational pull stretches Earth.
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Tidal Friction
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Tidal friction gradually slows Earth's rotation (and makes the Moon get
farther from Earth).
The Moon once orbited faster (or slower); tidal friction caused it to
''lock'' in synchronous rotation.
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Gravity Rules!
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The gravitational influence of the Moon cause the
tides
Leaving the surface of Earth takes a lot of energy,
it is like crawling out of a deep well. The escape
velocity is about 40,000 km/hr.
While the other fundamental forces
(electromagnetic, strong and weak) are much
stronger, their range is short and the motion of the
stars and galaxies are bound by gravity.
Free Fall
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Why are astronauts weightless in
space?
They are in a constant state of free
fall.
The Force from gravity in the space
station from Earth is not much less
than on the surface!